An ecological and evolutionary perspective on the parallel invasion of two cross-compatible trees. (18th August 2015) - Besnard, Guillaume
Abstract : The cultivated olive is an iconic Mediterranean crop that has been spread over the world in all regions with a Mediterranean climate. The species is however able to escape from cultivation, and can invade new ranges with negative impacts on native vegetation. The parallel invasion of two olive subspecies in different climatic zones of Australia provides an interesting case study of invasion, characterised by early genetic admixture between domesticated and wild taxa. In this synthesis, we provide an overview of the history and ecology of invasive olives, and identify further research needed to guide future management and invasion risk. Abstract: Invasive trees are generally seen as ecosystem-transforming plants that can have significant impacts on native vegetation, and often require management and control. Understanding their history and biology is essential to guide actions of land managers. Here, we present a summary of recent research into the ecology, phylogeography and management of invasive olives, which are now established outside of their native range as high ecological impact invasive trees. The parallel invasion of European and African olive in different climatic zones of Australia provides an interesting case study of invasion, characterized by early genetic admixture between domesticated and wild taxa. Today, the impact of the invasive olives on native vegetation and ecosystem function is of conservation concern, with European olive a declared weed in areas of South Australia, and African olive a declared weed in New South Wales and Pacific islands. Population genetics was used to trace the origins and invasion of both subspecies in Australia, indicating that both olive subspecies have hybridized early after introduction. Research also indicates that African olive populations can establish from a low number of founder individuals even after successive bottlenecks. Modelling based on distributional data from the native and invasive range identified a shift of the realized ecological niche in the Australian invasive range for both olive subspecies, which was particularly marked for African olive. As highly successful and long-lived invaders, olives offer further opportunities to understand the genetic basis of invasion, and we propose that future research examines the history of introduction and admixture, the genetic basis of adaptability and the role of biotic interactions during invasion. Advances on these questions will ultimately improve predictions on the future olive expansion and provide a solid basis for better management of invasive populations.